Buying a Canon DSLR
Since you're still using the 300D, I'm guessing you're not so much into sport photography, so the extra speed that the upcoming 60D will give you over the 500D might not be that important to you. However, you do get a bit better ergonomics, with the extra display and wheel.
Depending on how much money you've spent on cards and batteries, it might be relevant to note that the 5D2 and the current 50D (we don't know yet about the 60D) will take your current CF cards, the 500D requires new SD cards (but then again, cards are cheap today). As for batteries, the current 50D (and maybe the future 60D) will take the BP-511 batteries from your 300D, the 500D and 5D2 will not.
introduce a tablet later in the year I might bide my time for a couple of months
I'd like to use the dslr remote app. but requires a microsoft platform to run on..